The present invention relates to the abrading of substrates and, more particularly, relates to the abrading of ceramic and semiconductor substrates using a small, computer-controlled abrading tool.
Ceramic substrates comprising ceramic material and metallization, useful for mounting semiconductor devices, often become nonplanar after sintering due to an uneven distribution of metal and ceramic materials within the ceramic substrate. Ceramic substrates useful for thin films require a planar ceramic substrate so any nonplanarity in the ceramic substrate is removed through polishing of the ceramic substrates. Polishing is typically accomplished by placing the ceramic substrates on a large polishing table wherein a slurry containing an abrasive grit is used as the abrasive medium.
As part of the manufacturing process of semiconductor devices, semiconductor wafers are polished by a chemical mechanical polishing (CMP) process, one example of which is disclosed in Trojan et al. U.S. Pat. No. 5,899,798, the disclosure of which is incorporated by reference herein. The uniform removal of material from and the planarity of patterned and unpatterned wafers is critical to wafer process yield. Generally, the wafer to be polished is mounted on a substrate carrier which holds the wafer using a combination of vacuum suction or other means to contact the rear side of the wafer and a retaining lip or ring around the edge of the wafer to keep the wafer centered on the substrate carrier. The front side of the wafer, the side to be polished, is then contacted with a chemically reactive slurry.
The amount of material removal is more critical in the planarizing of semiconductor wafers than ceramic substrates. Overpolishing (removing too much) or underpolishing (removing too little) of the wafer results in scrapping or rework of the wafer, respectively, which can be very expensive. To remedy this problem, a number of endpoint detect methods have been devised to detect when the desired endpoint for removal has been reached, and the polishing can be stopped. One such method for endpoint detect in a CMP process is disclosed in Li et al. U.S. Pat. 5,644,221, the disclosure of which is incorporated by reference herein.
While the above methods for planarization work well enough, the present invention takes a new approach to planarization of ceramic substrates and semiconductor wafers. Instead of large polishing pads or surfaces which planarize the entire ceramic substrate or semiconductor wafer at the same time, it would be desirable to have a method and apparatus for planarizing a small portion of the ceramic substrate or semiconductor wafer at any given time. This would allow greater versatility in the process, particularly if only small portions of the ceramic substrate or semiconductor wafer need to be abraded or otherwise require material removal.
Accordingly, it is a purpose of the present invention to have a method and apparatus for abrading a small portion of the ceramic substrate or semiconductor wafer at any given time.
It is another purpose of the present invention to have a method and process for abrading a ceramic substrate or semiconductor wafer which is versatile in use.
These and other purposes of the present invention will become more apparent after referring to the following description of the invention considered in conjunction with the accompanying drawings.
The purposes of the invention have been achieved by providing, according to a first aspect of the invention, an apparatus for abrading a substrate comprising:
a moveable abrading tool having at least one bur for abrading the substrate;
a stage for supporting the substrate; and
at least one height sensing device in communication with the abrading tool to determine a vertical position of the at least one bur with respect to the substrate.
According to a second aspect of the invention there is provided an apparatus for abraiding a substrate comprising:
a moveable,pneumatically-powered abraiding the substrate;
a stage for supporting the substrate; and
at least one laser intterferometer in communication with the abraiding tool to determine a vertical position of the at least one bur with respect to the substrate.
According to a third aspect of the invention there is provided an apparatus for abrading a substrate with an apparatus comprising a moveable abrading tool having at least one bur for abrading the substrate, a stage for supporting the substrate, and at least one height sensing device in communication with the abrading tool to determine a vertical position of the at least one bur with respect to the substrate, the method comprising the steps of:
moving the abrading tool across the substrate so as to abrade the substrate;
determining the vertical position of the at least one bur with the at least one height sensing device; and
communicating the vertical position of the at least one bur to the abrading tool.